The idea of having a dose counter is well known in the art, and a number of potential implementations for such a counter exist. U.S. Pat. No. 5,363,842 describes an inhaler which detects how much air is inhaled through it and during what course of time, including such measurements as the triggering of the release of aerosol, and also incorporates a dose counter.
U.S. Pat. No. 5,411,173 describes a counter device attachment for a depressible spray dispenser for products such as medicine. The dispenser comprises a clip to fit about the side wall of the dispenser's casing, a foot-leg positioned beneath the dispenser and connected to the clip, and a counter actuated by the shaft which moves within a shaft housing, wherein a button on the counter is incremented each time the tank is depressed.
U.S. Pat. No. 5,482,030 describes a counter for a spray container implementing a counting disk showing the number of activations. U.S. Pat. Nos. 5,544,647 and 5,622,163 describe an electronic counting device mounted on the exterior of the housing, which indicates the number of doses remaining in the canister as signaled by a switch activated by the canister movement.
U.S. Pat. No. 5,505,192 describes an electronic dispenser monitoring circuit mounted on the canister, comprising an elastomeric membrane switch which serves to count the number of doses given. U.S. Pat. No. 5,676,129 describes a dose counter based on the use of a miniature pressure sensor which detects the pressure pulse in the transfer channel of the mouthpiece of the MDI through which the inhaler dose is released. U.S. Pat. No. 5,809,997 describes a dose counter attached to the inhaler housing incorporating a strain gauge sensing extending through a hole in a side of the housing for engaging a portion of the canister next to the valve stem. The sensing arm senses when the valve stem of the canister is properly compressed for release of medication.
U.S. Pat. No. 6,029,659 describes an inhaler inside a housing of which a dose counter is activated by a push button that is depressed when force is applied to the canister. U.S. Pat. No. 6,138,669 describes the use of a miniature pressure sensor and microprocessor to detect the pressure pulse in the transfer channel of the mouthpiece of the MDI through which the inhaler dose is released. U.S. Pat. No. 6,283,365 describes a dose counter attached or attachable to the base of the canister, comprising a spring-loaded cap which is depressed in relation to a second part mounted on the domed base of the canister. Within the cap is a pair of independently rotatable rings, where each depression of the cap relative to the canister, causes the first ring to rotate and thus implement a mechanical counter. U.S. Pat. No. 6,405,727 describes a dose counting mechanism based on a wheel with a toothed disc portion and a smooth disc, the smooth disc of the wheel bearing digits 00 to 20 and the wheel bearing digits 0 to 9. When the wheels are viewed the display can show any number from 000 to 209.
U.S. Pat. No. 6,431,168 describes a mechanical, cog-based, dose indicator located within the base of the inhaler housing, by the outlet of the canister. U.S. Pat. No. 6,446,627 describes a dose indicator based on a rotary gear which moves in step-wise fashion in response to displacement of an actuator, where the rotary gear comprises a wheel having a plurality of ratchet teeth. U.S. Pat. No. 6,659,307 describes a dose counter comprising at least one flexible rotary counting element applied against and turning on a curved support surface.
U.S. Pat. No. 6,761,161 describes a dose counter comprising a ratchet wheel, a drive member selectively engaging the indicating member, a pawl selectively engaging the ratchet wheel, and a non-return member adapted to selectively engage the ratchet wheel so as to maintain a unidirectional rotation of the ratchet wheel. In one embodiment, the indicating device also includes a usage indicator member having usage indicia that indicates the number of usage cycles completed or remaining for the indicating device.
U.S. Pat. No. 7,331,340 describes an inhaler for use with a removable pressurized aerosol canister, having a display for indicating to a user the state of the canister. A memory device on the canister (or a housing which houses the canister) stores information indicative of doses dispensed from, or remaining in, the canister, where that information is processed to provide and display information representative of the state of the canister. US 20040255936 describes a disposable dose counter. US 20060254581 describes a counter module affixed to a MDI canister, and is thus differentiated from an embodiment in which the counter is affixed or built into an actuator body. The visual display is read from above the inhaler, or from a direction that is generally radial with respect to the major axis of the inhaler. Relative motion of the canister within the actuator body activates a switch component of the EDC module by means of a trigger mechanism positioned within a cap that is fixedly mounted to the canister.
US 20070295329 also describes an electronic counter module mounted on the base of the canister, where depression of the top of this module closes two contacts separated by a spring. The spring ensures that sufficient force is developed before the counter is incremented. US 20080017193 describes a dose counter comprising a sensor for directly detecting a metered medicament dose dispensed from said container through its outlet, and a visual display unit for displaying the number of metered doses of medicament used or remaining within the container.
U.S. Pat. No. 7,587,988 describes a mechanical dose indicator comprising a counter housing, a rocker arm with a pawl, the rocker arm being pivotally supported by the housing and arranged to perform a rocker movement in response to a linear actuation motion, a return spring for resetting the rocker arm, a ratchet wheel engageable with the pawl to convert the movement of the rocker arm into an incremental rotational motion of an axle arrangement, thus advancing a display means.
US 20080066742 describes a mechanical counting mechanism where the display arrangement is of pointer-gauge type with a static display section provided as an integrated part of a transparent display containing part of a counter housing. U.S. Pat. No. 7,637,227 describes a inhaler device counter for displaying remaining doses of medicine having a pointer gauge type display, integrally formed with the counter housing. US 2009139516 describes a dose counter for an inhaler having a count wheel with fixed index tooth arranged for intermittent meshing with kick teeth, such that rotation of a kick wheel results from rotation of the count wheel when intermittent meshing occurs.
Thus the prior art is broadly divided into (a) mechanical solutions with some kind of dial which is advanced mechanically after each depression of the canister, and (b) electronic devices showing the number of doses remaining on an LCD or such like. The electronic type of dose counter is further divided into those which sense the aerosol dose being released (for example using a pressure sensor located adjacent to the aerosol outlet), and those based on a switch which is actuated upon the physical depression of the canister. In the latter type, the travel or physical movement between the open and the closed position of the switch takes place either between the canister and its housing (i.e. the inhaler) or between two parts of a module attached to the canister. In either case, it is the physical travel associated with the physical depression of the canister which closes the switch and thus increments the dose counter. As with any dose counter that is not actually verifying the release of the dose but is merely based on the travel detected, there is a possibility of false positives or false negatives.